In recent years, advances in fuel systems for internal combustion engines, and particularly for diesel engines, have increased dramatically. However, in order to achieve optimal engine performance at all operating conditions with respect to fuel economy, exhaust emissions, noise, transient response, and the like, further advances are necessary. As one example, operational accuracy with electronically controlled fuel systems can be improved by reducing variations in injected fuel quantities.
A number of techniques, are known for reducing injected fuel quantity variations such as, for example, robust system design, precision manufacturing, precise component matching, and electronic control strategies. However, conventional manufacturing approaches for improving performance, such as tightening tolerances and the like, are typically cost prohibitive, and conventional control approaches such as open-loop look-up tables have become increasingly complex and difficult to implement as the number of degrees of freedom to control have increased, particularly with multiple-input, multiple-output (MIMO) control systems. In fact, both of these approaches improve accuracy only during engine operation immediately after calibration in a controlled environment, and neither compensate for deterioration or environmental noise changes, which affect subsequent performance. Closed-loop control systems for controlling injected fuel quantity variations are accordingly preferable, but typically require additional sensors to measure appropriate control parameters.
One known technique for implementing such a closed-loop control system without implementing additional sensors is to leverage existing information to estimate injected fuel quantity; i.e., implementation of a so-called “virtual sensor.” One example of a known control system 10 including such a virtual sensor is illustrated in FIG. 3. Referring to FIG. 3, system 10 includes a two-dimensional look-up table 14 receiving an engine speed/position signal via signal line 12 and a desired fuel injection quantity value from process block 16 via signal path 18. Table 14 is responsive to the engine speed/position signal and the desired fuel injection quantity value to produce an initial fueling command as is known in the art. The virtual injected fuel quantity sensor in system 10 typically comprises a two-dimensional look-up table 20 receiving the engine speed/position signal via signal path 12 and a fuel pressure signal from signal path 22. Table 20 is responsive to the fuel pressure and engine speed/position signals to produce an injected fuel quantity estimate that is applied to summing node 24. Node 24 produces an error value as a difference between the desired fuel injection quantity and the injected fuel quantity estimate and applies this error value to a controller 26. Controller 26 is responsive to the error value to determine a fuel command adjustment value, wherein the Initial fueling command and the fuel command adjustment value are applied to a second summing node 28. The output of summing node 28 is the output 30 of system 10 and represents a final fueling command that is the initial fueling command produced by table 14 adjusted by the fuel command adjustment value produced by controller 26.
While system 10 of FIG. 3 provides for a closed-loop fuel control system utilizing a virtual sensor to achieve at least some control over variations in injected fuel quantities, it has a number of drawbacks associated therewith. For example, a primary drawback is that prior art systems of the type illustrated in FIG. 3 are operable to compensate for variations in only a single operating parameter. Control over variations in additional parameters would require prohibitively large and difficult to manage multi-dimensional look-up tables, wherein such tables would be limited to only operating parameters capable of compensation via look-up table techniques. For operating parameters that deteriorate or change with time, for example, compensation via look-up tables simply does not work without some type of scheme for updating such tables to reflect changes in those operating parameters.
As another drawback of prior art systems of the type illustrated in FIG. 3, such systems are not closed-loop with respect to injector-to-injector fueling variations. For example, referring to FIG. 16, a plot 35 of measured fuel injection quantity vs. injector actuator commanded on-time (i.e., desired fueling command) for each injector (cylinder) of a six-cylinder engine, is shown wherein the between-cylinder fueling variations are the result of various mismatches in the fueling system hardware. As is apparent from plot 35, the between-cylinder fuel injection quantity variations are quite pronounced and generally unacceptable in terms of accurate fueling control. While known cylinder balancing techniques could reduce such cylinder-to-cylinder fueling variations, the fuel control system of FIG. 3 would be ineffective in reducing such variations. Moreover, the fuel control system of FIG. 3 would further be ineffective in reducing engine-to-engine fueling variations. Referring to FIG. 17, for example, plots of average injected fuel vs. injector on-time for three engine fueling extremes are illustrated. Nominal engine fueling requirements are illustrated by curve 36, minimum engine fueling conditions are illustrated by curve 38 and maximum engine fueling conditions are illustrated by curve 40. While engines of the same type may be designed for identical fueling requirements, their actual fueling requirements may fall anywhere between curves 38 and 40. Unfortunately, the prior art fuel control system of FIG. 3 cannot compensate for such engine-to engine fueling variations. In general, if such control parameter variations are not attributable to the operating parameter for which the system is designed to compensate for, but are instead attributable to other error sources for which the control system of FIG. 3 is not designed to compensate for, the system performance may actually be worse than would otherwise be the case with conventional fuel control techniques.
By the nature of their uses in a wide variety of applications, engines are typically required over their operating lifetimes to work in environments wherein many internal and external parameters that affect engine performance may vary, cannot be controlled and/or cannot be, or typically are not, measured. Heretofore, known control systems have attempted to improve injected fueling accuracy using a parameter that is both measurable and controllable. Such systems typically operate by making control changes, based on an estimated sensitivity in the fueling quantity, to this measurable and controllable parameter using assumed values for other internal and/or external parameters rather than taking into account performance effects and interactions of these other parameters. By contrast, if the injected fueling quantity can be estimated utilizing a sensor or virtual sensor that is independent of many of the internal and external parameters that affect the engine's injected fueling quantity, a robust closed-loop fueling quantity control can be performed directly on the estimated fuel quantity rather than on only one of the control parameters that affect the fueling quantity. What is therefore needed is an improved strategy for adaptively estimating injected fuel quantities based on real-time performance of certain fuel system operating conditions throughout an injection event to thereby allow for robust and accurate operation as well as straightforward integration into complex fuel control systems. Ideally, such a strategy should be capable of minimizing between-cylinder and between-engine fueling variations.